Powdery cement composition and method for producing the same

Abstract

To provide a powdered cement composition which contains ground clinker, gypsum, and limestone fine powder, and in which the proportion of an aluminate phase in the ground clinker is 5 mass% or more, and which has excellent sulfate resistance despite the high proportion of limestone fine powder.SOLUTION: There is provided a powdery cement composition which contains a crushed clinker, gypsum, and limestone fine powder, in which the crushed clinker contains 58 to 68 mass% of alite, 12 to 19 mass% of belite, 5 to 10 mass% of an aluminate phase, and 7 to 13 mass% of a ferrite phase in terms of calculated values according to the Bogue formula, the proportion of SO3 in the composition is 2.2 to 3.2 mass%, the proportion of powder having a grain size of 10 μm or less is 65 mass% or more in the limestone fine powder, the amount of the limestone fine powder is 5 to 11 pts.mass relative to the total of 100 pts.mass of the crushed clinker and the gypsum, and the Blaine specific surface area of the composition is 3,700 to 5,000 cm2 / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a powdered cement composition (particularly one containing limestone fine powder) and a method for producing the same. [Background technology]

[0002] Following the adoption of the Paris Agreement in 2015, the Japanese government declared in 2020 that it would aim to achieve carbon neutrality by 2050. In response to this declaration, the construction industry is actively promoting the use of blast furnace cement, fly ash cement, etc. to reduce the amount of clinker used and to cut carbon dioxide emissions during concrete production. However, production of blast furnace slag powder and fly ash, which are the ingredients of blast furnace cement and fly ash cement, may decrease in the future due to the downsizing of the steel mills and coal-fired power plants that are their production sources. For this reason, there is a demand for technology that can reduce the amount of clinker used without using ground granulated blast furnace slag or fly ash.

[0003] On the other hand, various cement compositions containing limestone fine powder are known. For example, Patent Document 1 describes a cement composition containing high-early-strength Portland cement and limestone fine powder, in which the content of the limestone fine powder is 20 to 60 mass %. This cement composition suppresses the generation of heat of hydration over a long period of time, and can prevent cracks caused by the accumulation of heat of hydration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-93951 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, by including limestone fine powder in the cement composition, the generation of heat of hydration can be suppressed. However, there is a problem in that the greater the amount of limestone fine powder added, the worse the sulfate resistance of the hardened product of the cement composition (for example, concrete). Here, sulfate resistance refers to the ability of concrete to maintain excellent durability for a long period of time without significantly expanding when in contact with groundwater or the like containing a high content of sulfates.

[0006] On the other hand, sulfate-resistant Portland cement, in which the proportion of aluminate phase is adjusted to 4 mass % or less, is known as cement having excellent sulfate resistance. However, if the proportion of the aluminate phase is 4 mass % or less, the cement composition will have a problem of poor early strength development. Therefore, in order to ensure excellent early strength development, it is necessary to use ground clinker in which the proportion of the aluminate phase is 5% by mass or more. An object of the present invention is to provide a powdered cement composition which contains ground clinker, gypsum, and limestone fine powder, and in which the proportion of an aluminate phase in the ground clinker is 5 mass% or more, and which has excellent sulfate resistance despite the high proportion of limestone fine powder, and a method for producing the same. [Means for solving the problem]

[0007] As a result of extensive research into solving the above problems, the present inventors have discovered that excellent sulfate resistance can be achieved by using a powdered cement composition that satisfies certain conditions, such as the proportion of powder having a particle size of 10 μm or less in the limestone fine powder being within a specific range, and have completed the present invention.

[0008] The present invention provides the following [1] to [5]. [1] A powdered cement composition comprising ground clinker, gypsum, and limestone fine powder, wherein the ground clinker contains, as calculated by the Bogue formula, 58 to 68 mass% of alite, 12 to 19 mass% of belite, 5 to 10 mass% of an aluminate phase, and 7 to 13 mass% of a ferrite phase; the proportion of SO3 in the powdered cement composition is 2.2 to 3.2 mass%; the proportion of powder having a particle size of 10 μm or less in the limestone fine powder is 65 mass% or more; the amount of the limestone fine powder is 5 to 11 mass parts per 100 mass parts of the total amount of the ground clinker and the gypsum; and the Blaine specific surface area of ​​the powdered cement composition is 3,700 to 5,000 cm 2 / g of a powdered cement composition. [2] The powdered cement composition according to [1] above, wherein the proportion of powder having a particle size exceeding 20 μm in the limestone fine powder is 18 mass % or less. [3] The powdery cement composition according to [1] or [2] above, wherein the total amount of gypsum dihydrate and anhydrous gypsum in the gypsum is 50 mass% or more. [4] The powdered cement composition according to any one of [1] to [3] above, which does not contain fly ash, ground granulated blast furnace slag, or silica fume, or which contains one or more selected from fly ash, ground granulated blast furnace slag, and silica fume in a total amount of 5 mass% or less. [5] A method for producing the powdered cement composition according to any one of [1] to [4] above, wherein raw materials for the powdered cement composition include cement clinker granules, unground gypsum, and limestone granules, and the method comprises a grinding step of simultaneously grinding the cement clinker granules, the unground gypsum, and the limestone granules to obtain the powdered cement composition. [Effects of the Invention]

[0009] The powdered cement composition of the present invention has excellent sulfate resistance despite the high proportion of limestone fine powder. Furthermore, the powdery cement composition of the present invention contains ground clinker with an aluminate phase ratio of 5% by mass or more, and therefore has excellent early strength development (for example, high compressive strength at 1 day old). DETAILED DESCRIPTION OF THE INVENTION

[0010] The powdered cement composition of the present invention is a powdered cement composition containing ground clinker, gypsum, and limestone fine powder, wherein (a) the ground clinker contains, as calculated by the Bogue formula, 58 to 68 mass% of alite, 12 to 19 mass% of belite, 5 to 10 mass% of an aluminate phase, and 7 to 13 mass% of a ferrite phase; (b) the proportion of SO3 in the powdered cement composition is 2.2 to 3.2 mass%; (c) the proportion of powder having a particle size of 10 μm or less in the limestone fine powder is 65 mass% or more; (d) the amount of limestone fine powder is 5 to 11 mass parts per 100 mass parts of the total amount of the ground clinker and gypsum; and (e) the Blaine specific surface area of ​​the powdered cement composition is 3,700 to 5,000 cm. 2 / g.

[0011] [Clinker crushing material] The ground clinker used in the present invention is obtained by grinding cement clinker, which is the main raw material for cement. In the present invention, the mineral composition of the pulverized clinker is calculated by the Bogue formula and is as follows: The proportion of alite (chemical formula: 3CaO SiO2; sometimes abbreviated as C3S) is 58 to 68 mass%, preferably 58.5 to 67 mass%, and more preferably 59 to 66 mass%. If this proportion is less than 58 mass%, the early strength development (for example, high compressive strength at ages of 7 to 14 days) decreases. If this proportion exceeds 68 mass%, the proportion of the aluminate phase decreases, which may decrease the early strength development.

[0012] The proportion of belite (chemical formula: 2CaO SiO2; sometimes abbreviated as C2S) is 12 to 19 mass%, preferably 13 to 18 mass%, and more preferably 14 to 17 mass%. If the proportion is less than 12 mass%, the long-term strength development (for example, high compressive strength after 28 days of age) decreases. If the proportion exceeds 19 mass%, the proportions of the aluminate phase and alite decrease, which may decrease the early strength development and early strength development. The proportion of the aluminate phase (chemical formula: 3CaO·Al2O3; sometimes abbreviated as C3A) is 5 to 10 mass %. From the viewpoint of obtaining excellent early strength development, the proportion of the aluminate phase is preferably 6% by mass or more, more preferably 7% by mass or more, and particularly preferably 8% by mass or more. From the viewpoint of obtaining excellent sulfate resistance, the proportion of the aluminate phase is preferably 9 mass % or less, more preferably 8 mass % or less, and particularly preferably 7 mass % or less. The proportion of the ferrite phase (chemical formula: 4CaO·Al2O3·Fe2O3; sometimes abbreviated as C4AF) is 7 to 13 mass%, preferably 8 to 12 mass%. If this proportion is less than 7 mass%, chemical resistance decreases. If this proportion exceeds 13 mass%, the proportion of other minerals (for example, aluminate phase) decreases, which may result in a decrease in early strength development.

[0013] The proportions of alite (C3S), belite (C2S), aluminate phase (C3A), and ferrite phase (C4AF), which are the mineral composition of the ground clinker, are calculated using the following Bogue formulas (1) to (4). (1) C3S(mass%)=(4.07×CaO(mass%))-(7.60×SiO2(mass%))-(6.72×Al2O3(mass%))-(1.43×Fe2O3(mass%)) (However, in formula (1), the value of "CaO (mass%)" does not include free lime.) (2) C2S(mass%)=(2.87×SiO2(mass%))-(0.754×C3S(mass%)) (3) C3A(mass%)=(2.65×Al2O3(mass%))-(1.69×Fe2O3(mass%)) (4) C4AF(mass%)=3.04×Fe2O3(mass%)

[0014] [plaster] In the present invention, the gypsum used is at least one selected from the group consisting of gypsum dihydrate, gypsum anhydride, and gypsum hemihydrate. In terms of sulfate resistance and the like, the proportion of the total amount of gypsum dihydrate and anhydrous gypsum in the total amount of gypsum (100% by mass) is preferably 50% by mass or more, and more preferably 60% by mass or more. The amount of gypsum is an amount that makes the proportion of SO3 in the powdered cement composition 2.2 to 3.2 mass%. For example, if the amount of SO3 contained in the ground clinker is 0.7 mass% in terms of the proportion in the powdered cement composition (see Clinker A in Table 1 below), and the amount of gypsum is set to be 1.9 mass% in terms of the proportion in the powdered cement composition, the total will be 2.6 mass% (see Example 1 in Table 3 below).

[0015] [Fine limestone powder] The limestone fine powder used in the present invention has a ratio of powder having a particle size of 10 μm or less of 65% by mass or more (preferably 70% by mass or more). The upper limit of this proportion is not particularly limited, but is preferably 90% by mass from the viewpoint of ease of pulverization and the like. In the total amount (100% by mass) of the limestone fine powder, the proportion of powder having a particle size of more than 10 μm and not more than 20 μm is preferably not more than 30% by mass, more preferably not more than 20% by mass. In the total amount (100% by mass) of the limestone fine powder, the proportion of powder having a particle size exceeding 20 μm is preferably 18% by mass or less, more preferably 15% by mass or less. In the present invention, when the limestone fine powder has the above particle size distribution, the sulfate resistance of the powdery cement composition can be improved.

[0016] The amount of limestone fine powder is 5 to 11 parts by mass, preferably 5 to 10 parts by mass, more preferably 5 to 9 parts by mass, even more preferably 6 to 8 parts by mass, and particularly preferably 6 to 7 parts by mass, relative to 100 parts by mass of the total amount of the ground clinker and gypsum. When the amount is 5 parts by mass or more, the amount of ground clinker can be reduced by the amount of increased limestone fine powder, thereby further reducing carbon dioxide emissions during concrete production.When the amount is 11 parts by mass or less, the sulfate resistance of the powdered cement composition can be further improved.

[0017] [Other materials] The powdered cement composition of the present invention may contain other powders in addition to ground clinker, gypsum, and fine limestone powder. Other examples of powdery materials include fly ash, ground granulated blast furnace slag, and silica fume. The proportion of the total amount of other powdery materials in the total amount (100% by mass) of the powdery cement composition is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass.

[0018] [Particle size of powdered cement composition] The Blaine specific surface area of ​​the powdered cement composition of the present invention is preferably 3,700 to 5,000 cm 2 / g, more preferably 3,800 to 4,900 cm 2 / g, and particularly preferably 3,700 to 4,800 cm 2 / g. The value is 3,700 cm 2 If the value is less than 5,000 cm / g, the sulfate resistance of the powdered cement composition will decrease. 2 If the particle size exceeds 1 / g, the amount of work required for pulverization to obtain a powder having such a particle size becomes too great.

[0019] [Method for producing powdered cement composition] The raw materials for the powdery cement composition of the present invention include at least cement clinker granules, unground gypsum, and limestone granules. The cement clinker granules are coarsely crushed cement clinker, and can be obtained by crushing the cement clinker using a crushing means such as a jaw crusher to a maximum particle size of 5 mm or less. As the cement clinker granules, for example, those having a maximum particle size of 5 mm or less and having a proportion of granules with a particle size exceeding 20 μm of 95 mass % or more can be used. Cement clinker can be obtained by determining the types and amounts of various raw materials commonly used as raw materials for cement so as to obtain the mineral composition of the pulverized clinker described above, and then mixing and firing these various raw materials. As the unpulverized gypsum, one having a particle size that is common as a raw material for cement (in other words, one before being pulverized together with cement clinker) can be used. As the limestone particles, for example, those having a maximum particle size of 5 mm or less and containing 95 mass % or more of particles having a particle size exceeding 20 μm can be used.

[0020] A preferred example of a method for producing a powdery cement composition includes a grinding step in which cement clinker granules, unground gypsum, and limestone granules are simultaneously ground to obtain the powdery cement composition. By carrying out such simultaneous grinding, the sulfate resistance of the powdery cement composition can be further improved. In the present invention, the powdered cement composition is usually produced as a premix product. In this case, the powdered cement composition is mixed with aggregate, water, and other materials (e.g., admixtures) that are used as needed when preparing concrete, etc. [Example]

[0021] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [Materials for powdered cement composition] The following cement clinker granules, unground gypsum, and limestone granules were used as materials. (1) Cement clinker granules As cement clinker, clinkers A to C (3 types) having chemical compositions and mineral compositions shown in Tables 1 and 2 were used. Clinkers A to C (each with a maximum particle size of approximately 5 cm) were crushed using a jaw crusher (product name: BB300; manufacturer: Retsch) to obtain clinker granules A to C. Clinker granules A to C all had a maximum particle size of 1.2 mm or less, and the proportion of granules having a particle size exceeding 20 μm was 95 mass % or more. Clinker particles A, B, and C correspond to clinkers A, B, and C, respectively.

[0022] (2) Unground gypsum Four types of unground gypsum were used: (i) gypsum containing 100% by mass of gypsum dihydrate, (ii) gypsum containing 100% by mass of gypsum anhydrite, (iii) gypsum which is a mixture of 66% by mass of gypsum dihydrate and 34% by mass of gypsum hemihydrate, and (iv) gypsum which is a mixture of 71% by mass of gypsum dihydrate and 29% by mass of gypsum hemihydrate. The uncrushed gypsum (i) to (iv) were all obtained by roughly crushing gypsum with a maximum particle size of about 10 cm using a jaw crusher (product name: BB300; manufacturer: Recce). The unpulverized gypsum (i) to (iv) all had a maximum particle size of 1.2 mm or less, and the proportion of particles having a particle size exceeding 20 μm was 95 mass % or more.

[0023] (3) Limestone grains The limestone granules used had a maximum particle size of 1.2 mm or less and contained 99% or more by mass of particles with a particle size exceeding 20 μm. The calcium carbonate content in the limestone granules was 95% or more by mass. (4) Limestone powder A (material used in Comparative Examples 1 and 2) A fine limestone powder was used in which the proportion of powder having a particle size exceeding 20 μm was about 35 to 40 mass % (see "Particle size distribution (%) of fine limestone powder" in Comparative Examples 1 and 2 in Table 3). In Table 3, the particle size distribution (%) of the limestone fine powder in Comparative Example 1 and Comparative Example 2 differs slightly due to measurement errors. (5) Limestone fine powder B (material used in Comparative Example 3) A fine limestone powder was used in which the proportion of powder having a particle size exceeding 20 μm was about 20 to 25 mass % (see "Particle size distribution (%) of fine limestone powder" in Comparative Example 3 in Table 3).

[0024] [Example 1] Clinker granules A obtained by roughly crushing clinker A shown in Tables 1 and 2, uncrushed gypsum (gypsum dihydrate: 100% by mass), and limestone granules were charged into a ball mill and crushed simultaneously (also referred to as "simultaneous crushing" in this specification) to obtain a powdery cement composition. In this case, the amount of limestone granules was set to 6 parts by mass per 100 parts by mass of the total of clinker granules A and unground gypsum. The amount of unground gypsum was set to an amount such that the proportion of SO3 in the powdered cement composition, including SO3 derived from clinker A, would be 2.6% by mass. The obtained powdered cement composition was measured for (i) particle size distribution of the limestone fine powder, (ii) Blaine specific surface area of ​​the powdered cement composition, and (iii) expansion rate at 180 days when a hardened body of the powdered cement composition was immersed in a sodium sulfate solution by the following methods.

[0025] The particle size distribution of the limestone fine powder was obtained by sieving the powdered cement composition using sieves with opening sizes of 10 μm and 20 μm and a vacuum suction type sieving machine (product name: Air Jet Sieve e200LS; manufacturer: Hosokawa Micron Corporation), and then determining the amount of limestone components for each of the three resulting powders using TG-DTA. The amount of limestone component was calculated using the following formula (1). Amount of limestone component (mass%) = Q × 100 / 44 (1) (In formula (1), Q is the weight loss (decarbonation amount) (mass %) at 650 to 800°C.) The TG-DTA equipment and measurement conditions were as follows: (i) Product name of thermogravimetric analyzer: "Thermo plus EV02 TG8121" (manufactured by Rigaku Corporation) (ii) Measurement conditions Sample size: 20 mg Heating rate: 10℃ / min Nitrogen gas flow: 300 mL / min

[0026] The Blaine specific surface area of ​​the powdery cement composition was measured in accordance with the method described in "JIS R 5201:2015" (physical testing method for cement). The expansion coefficient of the hardened product of the powdery cement composition was measured in accordance with the method described in ASTM C 1012. The smaller the expansion coefficient, the better the sulfate resistance. The results are shown in Table 3. In Table 3, "Particle size distribution of limestone fine powder (%)" is based on mass and refers to "the proportion of powder having a particle size of 10 μm or less" ("up to 10 μm" in Table 3), "the proportion of powder having a particle size of more than 10 μm but not more than 20 μm" ("10-20 μm" in Table 3), and "the proportion of powder having a particle size of more than 20 μm" ("20 μm or more" in Table 3). Blaine specific surface area (cm 2 / g)" indicates the Blaine specific surface area of ​​the powdered cement composition. "Proportion (%) of SO3" indicates the proportion (mass%) of sulfur trioxide contained in the powdered cement composition. "Expansion rate (%) at 180 days" indicates the expansion rate according to the method described in the above-mentioned "ASTM C 1012."

[0027] [Example 2] An experiment was carried out in the same manner as in Example 1, except that the type of unground gypsum was changed to anhydrous gypsum. [Example 3] An experiment was conducted in the same manner as in Example 1, except that the type of clinker was changed to clinker B, the type of unground gypsum was changed to a mixture of gypsum dihydrate and gypsum hemihydrate (gypsum dihydrate: 66% by mass), and the amount of unground gypsum was determined so that the proportion of sulfur trioxide (SO3) in the powdered cement composition was 2.8% by mass. [Comparative Example 1] An experiment was conducted in the same manner as in Example 1, except that instead of the simultaneous grinding method, the clinker and unground gypsum were ground together to obtain cement, and then this cement was mixed with limestone fine powder A to obtain a powdered cement composition (also referred to as "separate grinding" in this specification). Comparative Example 2 An experiment was carried out in the same manner as in Example 2, except that separate grinding was used instead of simultaneous grinding. Comparative Example 3 An experiment was carried out in the same manner as in Example 3, except that separate grinding was used instead of simultaneous grinding. [Reference example 1] An experiment was conducted in the same manner as in Example 1, except that the type of clinker was changed to clinker C and the type of unground gypsum was changed to a mixture of gypsum dihydrate and gypsum hemihydrate (gypsum dihydrate: 71% by mass). The results are shown in Table 3.

[0028] [Table 1]

[0029] [Table 2]

[0030] [Table 3]

[0031] From Table 3, it can be seen that in Examples 1 to 3, although clinker pulverized material with an aluminate phase ratio of 5 mass% or more (see Clinkers A to B in Table 2) was used, the simultaneous grinding method was used when preparing the powdered cement composition, and as a result, the proportion of powder with a particle size of 10 μm or less in the particle size distribution of the limestone fine powder was larger than when the separate grinding method was used, and therefore the expansion rate at 180 days was very small and the sulfate resistance was excellent compared to Comparative Examples 1 to 3 (experimental examples using the separate grinding method). Furthermore, when comparing Example 3 with Reference Example 1, it can be seen that, although Example 3 uses a ground clinker with an aluminate phase ratio of 9.0 mass% (see Clinker B in Table 2), it achieves excellent sulfate resistance (both expansion coefficients are within the range of 0.05 to 0.06%) comparable to Reference Example 1, which uses a ground clinker with an aluminate phase ratio of 4.4 mass% (see Clinker C in Table 2).

Claims

1. A powdered cement composition comprising ground clinker, gypsum, and limestone fine powder, The clinker pulverized material contains, as calculated by the Bogue method, 58 to 68 mass% alite, 12 to 19 mass% belite, 5 to 10 mass% aluminate phase, and 7 to 13 mass% ferrite phase, SO in the powder cement composition ３ is 2.2 to 3.2 mass%, In the limestone fine powder, the proportion of powder having a particle size of 10 μm or less is 65 mass% or more, The amount of the limestone fine powder is 5 to 11 parts by mass per 100 parts by mass of the total amount of the clinker pulverized material and the gypsum, The Blaine specific surface area of ​​the powdered cement composition is 3,700 to 5,000 cm ２ / g.

2. 2. The powdered cement composition according to claim 1, wherein the proportion of powder having a particle size exceeding 20 μm in the limestone fine powder is 18% by mass or less.

3. 2. The powdery cement composition according to claim 1, wherein the total amount of gypsum dihydrate and anhydrous gypsum in the gypsum is 50% by mass or more.

4. 2. The powdered cement composition according to claim 1, wherein the powdered cement composition does not contain fly ash, ground granulated blast furnace slag, or silica fume, or contains one or more selected from fly ash, ground granulated blast furnace slag, and silica fume in a total amount of 5 mass% or less.

5. A method for producing the powdered cement composition according to any one of claims 1 to 4, comprising: The raw materials of the powdered cement composition include cement clinker granules, unground gypsum, and limestone granules; A method for producing a powdered cement composition, comprising a grinding step of simultaneously grinding the cement clinker granules, the unground gypsum, and the limestone granules to obtain the powdered cement composition.

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